Osama Bin Laden is still alive and leading a "holy war" against the West, according to a videotaped statement by his right-hand man.

Ayman al-Zawahri was speaking in a message posted on the internet and then broadcast by al-Jazeera.

It is not clear when the video, which shows the al-Qaeda figure speaking in a white room, was filmed.

He called for attacks on oil targets and said al-Qaeda was "spreading and expanding and strengthening".

News of Bin Laden's good health was a "message of joy to all Muslims", Mr Zawahri said.

Al-Qaeda, he said, was a "popular organisation confronting a new Crusader Zionist Western and Israeli campaign, in defence of all violated Muslim lands".

In Iraq, he said, the US-led coalition was "receiving blows each day", while the Iraqi government was "begging Americans not to leave because they know the day Americans leave is the day they are finished".

He urged attacks on oil installations in Islamic countries "because most of the revenues of this oil go to the enemies of Islam".

Ayman al-Zawahri, an eye surgeon by training, is seen as the chief ideologue of al-Qaeda.

He is believed by some experts to have been the "operational brains" behind the 11 September 2001 attacks in the United States.

He was number two - behind only Bin Laden - in the 22 Most Wanted Terrorists List announced by the US government in 2001 and has a $25m bounty on his head.